How to use the @opencensus/propagation-binaryformat.deserializeSpanContext function in @opencensus/propagation-binaryformat

static getSpanContext(metadata: grpcTypes.Metadata): SpanContext | null {
    const metadataValue = metadata.getMap()[GRPC_TRACE_KEY] as Buffer;
    // Entry doesn't exist.
    if (!metadataValue) {
      return null;
    }
    const spanContext = deserializeSpanContext(metadataValue);
    // Value is malformed.
    if (!spanContext) {
      return null;
    }
    return spanContext;
  }